1. Field of the Invention
The present invention relates to the technical field of touch panel and, more particularly, to a capacitive touch panel with high touching sensitivity.
2. Description of Related Art
Most of the current consumer electronic devices are provided with touch pads for use as input devices. In order to meet the light, thin and small features, a touch pad is mostly integrated with a panel as a touch panel for allowing convenient input. According to the sensing principle, the touch pad can be one of resistive type, capacitive type, acoustic wave type or optics type.
The operation principle of touch panels is to sense a voltage, a current, an acoustic wave or an infrared when a finger or other medium touches on a touch screen, so as to detect the coordinates of touching points. For example, a resistive touch panel uses the voltage difference between upper and lower electrodes to determine the location where a force is applied, to thereby detect the touching point. A capacitive touch panel uses the current or the voltage originated from capacitance changes in a static electricity combination of transparent electrodes in row and column with human body to detect the touching coordinate.
FIG. 1 is a schematic diagram of the structure of a prior capacitive touch panel, which is also disclosed in U.S. Pat. No. 4,550,221 granted to Mabusth for a “Touch sensitive control device”. The conductive plates 30 are disposed on a substrate 28 in fine metal, with a specific shape (such as diamond shape) formed by etching. As shown in FIG. 1, the conductive plates 30 form a first array in horizontal direction that has conductor lines X1-X12 respectively, and form a second array in vertical direction that has conductor lines Y1-Y12 respectively. Each of the conductor lines X1-X12, Y1-Y12 has a plurality of electrode plates disposed on the substrate in an interleaved and non-overlapped manner. Each diamond-shaped metal plate of conductor lines Y1-Y12 has at least two edges adjacent to the metal plates of conductor lines X1-X12, and at most four edges adjacent thereto. Similarly, each diamond-shaped metal plate of conductor lines X1-X12 has at least two edges adjacent to the metal plates of conductor lines Y1-Y12, and at most four edges adjacent thereto. A detector (not shown) detects the current changes of lateral induced capacitance between the conductor lines Y1-Y12 and X1-X12 when a driver (not shown) generates a driving signal, so as to detect the touching coordinates.
FIG. 2 is a schematic diagram of the structure of another typical capacitive touch panel. The conductive plates are disposed on the upper and lower sides of a substrate in fine metal. As shown in FIG. 2, the conductive plates form a first array at the lower side of the substrate in horizontal direction that has conductor lines X1,X2,X3 . . . , respectively, and form a second array at the upper side in vertical direction that has conductor lines Y1,Y2,Y3 . . . , respectively. Each of the conductor lines X1,X2,X3 . . . , Y1,Y2,Y3 . . . is disposed in an interleaved and non-overlapped manner. A detector 150 detects the current changes of ambient induced capacitance between the electrode plates 120 and 130 when a driver 140 generates a driving signal, to thereby detect the touching coordinates.
FIG. 3 is a schematic diagram of the structure of another prior touch panel, which is also disclosed in US Patent Publication No. 2009/0002337 entitled “Capacitive-type touch panel”. The conductive touch panel includes a transparent substrate 3, a plurality of first conductor lines 41 disposed on the substrate 3 in a first direction, and a plurality of second conductor lines 42 disposed on the substrate 3 in a second direction. The plurality of second conductor lines 42 and the plurality of first conductor lines 41 are intersected insulatively. Each of the first conductor lines 41 is intersected with and divided by the second conductor lines 42 into a series of first electrode regions 411. Each of the second conductor lines 42 is intersected with and divided by the first conductor lines 41 into a series of second electrode regions 412. The first and the second conductor lines 41 and 42 form a matrix of capacitance regions when a current is applied to the first conductor lines 41 and the second conductor lines 42. A controller 70 is electrically connected to the first and the second conductor lines 41 and 42 through conductive wires 61 and 62 for detecting the capacitance of the capacitance regions.
FIG. 4 is a schematic diagram of driving the typical capacitive touch panel of FIG. 2. The driver 140 generates a driving signal sequentially on the conductor lines X1-X12. The driving signal passes through the mutual capacitors Cm between the conductor lines X1-X12 and Y1-Y12 to thereby couple charge to the conductor lines Y1-Y12. The detector 150 uses a plurality of sensors 151 to measure charge amount to thereby calculate the capacitance values of the mutual capacitors Cm, where Cm 0 is set for no contact.
Since the electric lines between the conductor lines X1-X12 and Y1-Y12 may be interfered when a grounded conductor or finger approaches to the touch panel, the capacitance values of the mutual conductors Cm may be influenced. Further, the touching location can be determined by the change proportion (Cm0-Cm1)/Cm0 of the mutual capacitors Cm.
FIGS. 5A and 5B schematically illustrate the changes of the electric lines for the typical capacitive touch panel of FIG. 2. As shown in FIG. 5A, the electric lines are present in the overlapping region (A, A′) of the conductor lines X1 and Y1 when the driver 140 generates a driving signal on the conductor line X1, and in this case, Cm=Cm0. As shown in FIG. 5B, the finger can be regarded as a grounded object when a grounded object or finger approaches to the overlapping region of the conductor lines X1 and Y1, and the electric lines that are not shielded by the overlapping region A are influenced by the finger, thus in the case Cm=Cm 1, wherein Cm 1 is smaller than Cm0. Therefore, the change proportion of the mutual capacitors Cm equals to (Cm0-Cm1)/Cm0, and the sensors 151 accordingly determine the touching location. However, since many electric lines are shielded by the overlapping region A, the change proportion (Cm0-Cm1)/Cm0 is not significant. In this case, the sensitivity of the sensors 151 and the detection time should be increased to accumulate enough charge for being detected by the sensors 151.
Therefore, it is desirable to provide an improved capacitive touch panel with high touching sensitivity to mitigate and/or obviate the aforementioned problems.